Present digital satellite receivers usually comprise a tuner with an RF-input stage for receiving a plurality of digital satellite channels, a mixer for selecting and downconverting a wanted satellite channel into an intermediate frequency range or a baseband, and a demodulator, which converts the signal of the selected satellite channel into an appropriate television signal usable for a television set. Widely used are direct conversion satellite receivers, which have the advantage of high circuit integration with a low count for external components.
The mixer of a direct conversion receiver converts a selected television signal directly to a baseband signal, which is subsequently filtered by a baseband lowpass filter, digitized by an analog/digital converter and processed by the demodulator to a digital television signal. The tuner comprises a gain controlled RF amplifier and a gain controlled baseband amplifier, which are controlled by the demodulator for providing a gain variation of at least 50 dB, which is required for providing a high sensitivity of the satellite receiver and for an optimum performance of the demodulator.